Laughter is a primitive reflex common to most animals not just humans New Scientist - May 2002
Humans don't have a monopoly on laughter, says Silvia Cardoso. A behavioural biologist at the State University of Campinas, Brazil, she says it's a primitive reflex common to most animals: even rats laugh. Too little laughter could have serious consequences for our mental, physical and social well-being.
Laughter a universal phenomenon, and one of the most common things we do. We laugh many times a day, for many different reasons, but rarely think about it, and seldom consciously control it. We know so little about the different kinds and functions of laughter, and my interest really starts there. Why do we do it? What can laughter teach us about our positive emotions and social behaviour? There's so much we don't know about how the brain contributes to emotion and I think we can get at understanding this by studying laughter.
Only 10 or 20 per cent of laughing is a response to humor. Most of the time it's a message we send to other people--communicating joyful disposition, a willingness to bond and so on. It occupies a special place in social interaction and is a fascinating feature of our biology, with motor, emotional and cognitive components. Scientists study all kinds of emotions and behaviour, but few focus on this most basic ingredient. Laughter gives us a clue that we have powerful systems in our brain which respond to pleasure, happiness and joy. It's also involved in events such as release of fear.
My professional focus has always been on emotional behaviour. I spent many years investigating the neural basis of fear in rats, and came to laughter via that route. When I was working with rats, I noticed that when they were alone, in an exposed environment, they were scared and quite uncomfortable. Back in a cage with others, they seemed much happier. It looked as if they played with one another--real rough-and-tumble--and I wondered whether they were also laughing. The neurobiologist Jaak Panksepp had shown that juvenile rats make short vocalisations, pitched too high for humans to hear, during rough-and-tumble play. He thinks these are similar to laughter. This made me wonder about the roots of laughter.
Do you believe other animals laugh too?
You only have to look at the primates closest to humans to see that laughter is clearly not unique to us. I don't find this too surprising, because we're only one among many social species and there's no reason why we should have a monopoly on laughter as a social tool. The great apes, such as chimpanzees, do something similar to humans. They open their mouths wide, expose their teeth, retract the corners of their lips, and make loud and repetitive vocalisations in situations that tend to evoke human laughter, like when playing with one another or with humans, or when tickled. Laughter may even have evolved long before primates. We know that dogs at play have strange patterns of exhalation that differ from other sounds made during passive or aggressive confrontation.
But I think we need to be careful about over-interpreting panting behaviour in animals at play. It's nice to think of it as homologous to human laughter, but it could just be something similar but with entirely different purposes and evolutionary advantages.
Everything humans do has a function, and laughing is no exception. Its function is surely communication. We need to build social structures in order to live well in our society and evolution has selected laughter as a useful device for promoting social communication. In other words, it must have a survival advantage for the species.
Do you think we have 'laughter genes'?
I'm sure that laughter has been selected by evolution as a useful device for promoting social communication. But we have yet to discover which genes command the enormously complex chain of physiological events which accompany laughter generation.
How have people studied those events?
There have been some studies using advanced brain-imaging techniques such as positron emission tomography and functional magnetic resonance imaging, as well as older-style tests such as electro-encephalography. They've really helped us to understand which bits of the brain are involved in which bits of emotion--normal or abnormal.
What have they found?
The brain scans are usually done while people are responding to humorous material. You see brainwave activity spread from the sensory processing area of the occipital lobe, the bit at the back of the brain that processes visual signals, to the brain's frontal lobe. It seems that the frontal lobe is involved in recognising things as funny. The left side of the frontal lobe analyses the words and structure of jokes while the right side does the intellectual analyses required to "get" jokes. Finally, activity spreads to the motor areas of the brain controlling the physical task of laughing. We also know about these complex pathways involved in laughter from neurological illness and injury. Sometimes after brain damage, tumours, stroke or brain disorders such as Parkinson's disease, people get "stonefaced" syndrome and can't laugh.
I find it improbable that a purely psychological mass reaction would last so long and be so widespread. Sometimes people have fits of abnormal, inappropriate, unrestrained and uncontrollable laughter dissociated from any social or humour stimulus. Laughter involves motor, emotional and cognitive components, each one located in a specific part of the brain. The American neurologists Hanna and Antonio Damasio suggest that abnormal laughter occurs when structures in the basal part of the brain are damaged. The pathways that normally automatically adjust the execution of laughter to be appropriate to the stimulus for it are disrupted and the brain gets incomplete information about the cognitive and situational context of a potential stimulus--it gets it wrong about whether or not to laugh--resulting in chaotic behaviour. Based on this model, I suggest that a viral infection, probably some kind of encephalitis in the basal part of the brain, provoked the 1962 epidemic. Many of the people affected had fever, and some also had movement disturbances.
So is "normal" laughter hard-wired?
We see babies and children laughing with their mothers, and it's easy to assume that they're imitating. But we've studied children who have no opportunity to learn laughter, because they're congenitally blind, deaf, or mute, and found that they can smile and laugh even though they're unable to copy others. It's only the beginning of the story, though, and we need to know more about the differences between laughter in different people.
How is laughter different in people who are blind or deaf?
The groundbreaking study in this area was conducted by the human ethologist Irenaus Eibl-Eibsfeldt. He found that laughter and crying patterns are well-developed in such children. He concluded that these expressions evolved through natural selection. Deaf children have different sound patterns in their laughter, as they have in speech. Blind children seem not to display all the facial components of laughter. We're going to study these differences by statistically analysing the minute variations in laughter between different types of people. We'll video their faces while they laugh in response to various stimuli. Then we'll analyse every millisecond of their facial behaviour and vocalisation.
Does laughter differ between the sexes?
I'm sure it does, particularly the uses to which the sexes put laughter as a social tool. For instance, women smile more than laugh, and are particularly adept at smiling and laughing with men as a kind of "social lubricant". It might even be possible that this has a biological origin, because women don't or can't use their physical size as a threat, which men do, even if unconsciously.
And between cultures?
Cultural differences are certainly part of it. Loud, raucous laughter with exaggerated movements and expressions is considered "unfeminine" in most cultures, and is much more common among men, particularly if they're with other men. In several situations I see laughter used, apparently unconsciously, to help get things as diverse as power, friendship, a lover or truthful behaviour from subordinates. For instance, socially dominant individuals, from bosses to tribal chiefs, use laughter to control their subordinates. When the boss laughs, their minions laugh too. Laughter might be a form of asserting power by controlling the emotional climate of the group, and it also has a dark side. There are theories that laughter and aggression have common origins, with some kinds of laughter in primates apparently being threatening--just look at the way they bare their teeth. That might explain why being laughed at is so unpleasant.
Is it true that laughing can make us healthier?
It's undoubtedly the best medicine. For one thing, it's exercise. It activates the cardiovascular system, so heart rate and blood pressure increase, then the arteries dilate, causing blood pressure to fall again. Repeated short, strong contractions of the chest muscles, diaphragm and abdomen increase blood flow into our internal organs, and forced respiration--the ha! ha!--makes sure that this blood is well oxygenated.
Muscle tension decreases, and indeed we may temporarily lose control of our limbs, as in the expression "weak with laughter". It may also release brain endorphins, reducing sensitivity to pain and boosting endurance and pleasurable sensations. Some studies suggest that laughter affects the immune system by reducing the production of hormones associated with stress, and that when you laugh the immune system produces more T-cells. But no rigorously controlled studies have confirmed these effects. Laughter's social role is definitely important. I'm very concerned that today's children may be heading for a whole lot of social ills because their play and leisure time is so isolated and they lose out on lots of chances for laughter.
When children stare at computer screens, rather than laughing with each other, this is at odds with what's natural for them. Natural social behaviour in children is playful behaviour, and in such situations laughter indicates that make-believe aggression is just fun, not for real, and this is an important way in which children form positive emotional bonds, gain new social skills and generally start to move from childhood to adulthood. I think parents need to be very careful to ensure that their children play in groups, with both peers and adults, and laugh more.